1. Field of the Invention
The present invention relates generally to a power supply equipment backup system for interruption of service and more particularly to an inverter control system provided for a power supply equipment backup system for interruption of service, in which a power inverter is generally connected in parallel with a commercial AC power supply line in order to supply power from the inverter to a device load even when commercial AC power source fails.
2. Description of the Prior Art
Conventionally, power supply equipment backup system for interruption of service can roughly be classified into two types: DC switch type and floating type.
In the DC switch type, series-connected AC-DC converter (power rectifier) and a DC-AC converter (power inverter) are connected in parallel with a commercial AC power supply line; a battery is connected to the power inverter through a DC switch closed only when commercial AC power source is off; a constant-voltage battery charger is connected from the commercial AC power source to the battery to continuously charge the battery. Further, power is supplied continuously from only the power inverter through an AC switch even while the commercial AC power source is normal. In this type of power supply equipment backup system for interruption of service, however, there exist some shortcomings as follows:
(1) Since the power inverter is always in operation even while commercial AC power source is normal, the power efficiency is not sufficiently high, because the power rectifier loss is great.
(2) Since the power rectifier and the battery charger are incorporated within the equipment, the equipment is large in size and high in cost.
In the floating type, only a DC-AC converter (power inverter) is connected in parallel with a commercial AC power supply line; a battery is always connected to the power inverter; a constant-voltage battery charger is connected between the commercial AC power supply line and the battery to continuously charge the battery; a DC-DC converter and an automatic voltage regulator is provided for the battery. Similarly, power is supplied from only the power inverter through an AC switch even while the commercial AC power source is normal. In this type of power supply equipment backup system for interruption of service, however, there exist some drawbacks as follows:
(1) Since the power inverter is always in operation even while the commercial AC power source is normal and further the automatic voltage regulator always operates to keep the battery terminal voltage at a predetermined value as long as the commercial power source is normal, the power efficiency is not sufficiently high.
(2) Since the battery charger and the automatic voltage regulator are incorporated within the equipment, the equipment is large in size and high in cost.
A more detailed description of the prior-art power supply equipment backup system for interruption of service will be made hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.